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Diffstat (limited to 'libjava/classpath/external/jsr166/java/util/concurrent/FutureTask.java')
| -rw-r--r-- | libjava/classpath/external/jsr166/java/util/concurrent/FutureTask.java | 325 |
1 files changed, 325 insertions, 0 deletions
diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/FutureTask.java b/libjava/classpath/external/jsr166/java/util/concurrent/FutureTask.java new file mode 100644 index 000000000..94742405d --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/concurrent/FutureTask.java @@ -0,0 +1,325 @@ +/* + * Written by Doug Lea with assistance from members of JCP JSR-166 + * Expert Group and released to the public domain, as explained at + * http://creativecommons.org/licenses/publicdomain + */ + +package java.util.concurrent; +import java.util.concurrent.locks.*; + +/** + * A cancellable asynchronous computation. This class provides a base + * implementation of {@link Future}, with methods to start and cancel + * a computation, query to see if the computation is complete, and + * retrieve the result of the computation. The result can only be + * retrieved when the computation has completed; the <tt>get</tt> + * method will block if the computation has not yet completed. Once + * the computation has completed, the computation cannot be restarted + * or cancelled. + * + * <p>A <tt>FutureTask</tt> can be used to wrap a {@link Callable} or + * {@link java.lang.Runnable} object. Because <tt>FutureTask</tt> + * implements <tt>Runnable</tt>, a <tt>FutureTask</tt> can be + * submitted to an {@link Executor} for execution. + * + * <p>In addition to serving as a standalone class, this class provides + * <tt>protected</tt> functionality that may be useful when creating + * customized task classes. + * + * @since 1.5 + * @author Doug Lea + * @param <V> The result type returned by this FutureTask's <tt>get</tt> method + */ +public class FutureTask<V> implements RunnableFuture<V> { + /** Synchronization control for FutureTask */ + private final Sync sync; + + /** + * Creates a <tt>FutureTask</tt> that will upon running, execute the + * given <tt>Callable</tt>. + * + * @param callable the callable task + * @throws NullPointerException if callable is null + */ + public FutureTask(Callable<V> callable) { + if (callable == null) + throw new NullPointerException(); + sync = new Sync(callable); + } + + /** + * Creates a <tt>FutureTask</tt> that will upon running, execute the + * given <tt>Runnable</tt>, and arrange that <tt>get</tt> will return the + * given result on successful completion. + * + * @param runnable the runnable task + * @param result the result to return on successful completion. If + * you don't need a particular result, consider using + * constructions of the form: + * <tt>Future<?> f = new FutureTask<Object>(runnable, null)</tt> + * @throws NullPointerException if runnable is null + */ + public FutureTask(Runnable runnable, V result) { + sync = new Sync(Executors.callable(runnable, result)); + } + + public boolean isCancelled() { + return sync.innerIsCancelled(); + } + + public boolean isDone() { + return sync.innerIsDone(); + } + + public boolean cancel(boolean mayInterruptIfRunning) { + return sync.innerCancel(mayInterruptIfRunning); + } + + /** + * @throws CancellationException {@inheritDoc} + */ + public V get() throws InterruptedException, ExecutionException { + return sync.innerGet(); + } + + /** + * @throws CancellationException {@inheritDoc} + */ + public V get(long timeout, TimeUnit unit) + throws InterruptedException, ExecutionException, TimeoutException { + return sync.innerGet(unit.toNanos(timeout)); + } + + /** + * Protected method invoked when this task transitions to state + * <tt>isDone</tt> (whether normally or via cancellation). The + * default implementation does nothing. Subclasses may override + * this method to invoke completion callbacks or perform + * bookkeeping. Note that you can query status inside the + * implementation of this method to determine whether this task + * has been cancelled. + */ + protected void done() { } + + /** + * Sets the result of this Future to the given value unless + * this future has already been set or has been cancelled. + * This method is invoked internally by the <tt>run</tt> method + * upon successful completion of the computation. + * @param v the value + */ + protected void set(V v) { + sync.innerSet(v); + } + + /** + * Causes this future to report an <tt>ExecutionException</tt> + * with the given throwable as its cause, unless this Future has + * already been set or has been cancelled. + * This method is invoked internally by the <tt>run</tt> method + * upon failure of the computation. + * @param t the cause of failure + */ + protected void setException(Throwable t) { + sync.innerSetException(t); + } + + // The following (duplicated) doc comment can be removed once + // + // 6270645: Javadoc comments should be inherited from most derived + // superinterface or superclass + // is fixed. + /** + * Sets this Future to the result of its computation + * unless it has been cancelled. + */ + public void run() { + sync.innerRun(); + } + + /** + * Executes the computation without setting its result, and then + * resets this Future to initial state, failing to do so if the + * computation encounters an exception or is cancelled. This is + * designed for use with tasks that intrinsically execute more + * than once. + * @return true if successfully run and reset + */ + protected boolean runAndReset() { + return sync.innerRunAndReset(); + } + + /** + * Synchronization control for FutureTask. Note that this must be + * a non-static inner class in order to invoke the protected + * <tt>done</tt> method. For clarity, all inner class support + * methods are same as outer, prefixed with "inner". + * + * Uses AQS sync state to represent run status + */ + private final class Sync extends AbstractQueuedSynchronizer { + private static final long serialVersionUID = -7828117401763700385L; + + /** State value representing that task is running */ + private static final int RUNNING = 1; + /** State value representing that task ran */ + private static final int RAN = 2; + /** State value representing that task was cancelled */ + private static final int CANCELLED = 4; + + /** The underlying callable */ + private final Callable<V> callable; + /** The result to return from get() */ + private V result; + /** The exception to throw from get() */ + private Throwable exception; + + /** + * The thread running task. When nulled after set/cancel, this + * indicates that the results are accessible. Must be + * volatile, to ensure visibility upon completion. + */ + private volatile Thread runner; + + Sync(Callable<V> callable) { + this.callable = callable; + } + + private boolean ranOrCancelled(int state) { + return (state & (RAN | CANCELLED)) != 0; + } + + /** + * Implements AQS base acquire to succeed if ran or cancelled + */ + protected int tryAcquireShared(int ignore) { + return innerIsDone()? 1 : -1; + } + + /** + * Implements AQS base release to always signal after setting + * final done status by nulling runner thread. + */ + protected boolean tryReleaseShared(int ignore) { + runner = null; + return true; + } + + boolean innerIsCancelled() { + return getState() == CANCELLED; + } + + boolean innerIsDone() { + return ranOrCancelled(getState()) && runner == null; + } + + V innerGet() throws InterruptedException, ExecutionException { + acquireSharedInterruptibly(0); + if (getState() == CANCELLED) + throw new CancellationException(); + if (exception != null) + throw new ExecutionException(exception); + return result; + } + + V innerGet(long nanosTimeout) throws InterruptedException, ExecutionException, TimeoutException { + if (!tryAcquireSharedNanos(0, nanosTimeout)) + throw new TimeoutException(); + if (getState() == CANCELLED) + throw new CancellationException(); + if (exception != null) + throw new ExecutionException(exception); + return result; + } + + void innerSet(V v) { + for (;;) { + int s = getState(); + if (s == RAN) + return; + if (s == CANCELLED) { + // aggressively release to set runner to null, + // in case we are racing with a cancel request + // that will try to interrupt runner + releaseShared(0); + return; + } + if (compareAndSetState(s, RAN)) { + result = v; + releaseShared(0); + done(); + return; + } + } + } + + void innerSetException(Throwable t) { + for (;;) { + int s = getState(); + if (s == RAN) + return; + if (s == CANCELLED) { + // aggressively release to set runner to null, + // in case we are racing with a cancel request + // that will try to interrupt runner + releaseShared(0); + return; + } + if (compareAndSetState(s, RAN)) { + exception = t; + result = null; + releaseShared(0); + done(); + return; + } + } + } + + boolean innerCancel(boolean mayInterruptIfRunning) { + for (;;) { + int s = getState(); + if (ranOrCancelled(s)) + return false; + if (compareAndSetState(s, CANCELLED)) + break; + } + if (mayInterruptIfRunning) { + Thread r = runner; + if (r != null) + r.interrupt(); + } + releaseShared(0); + done(); + return true; + } + + void innerRun() { + if (!compareAndSetState(0, RUNNING)) + return; + try { + runner = Thread.currentThread(); + if (getState() == RUNNING) // recheck after setting thread + innerSet(callable.call()); + else + releaseShared(0); // cancel + } catch (Throwable ex) { + innerSetException(ex); + } + } + + boolean innerRunAndReset() { + if (!compareAndSetState(0, RUNNING)) + return false; + try { + runner = Thread.currentThread(); + if (getState() == RUNNING) + callable.call(); // don't set result + runner = null; + return compareAndSetState(RUNNING, 0); + } catch (Throwable ex) { + innerSetException(ex); + return false; + } + } + } +} |